This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The Baas Laboratory is interested in the cellular and molecular mechanisms that orchestrate microtubules during development. The Bass lab uses live-cell imaging of microtubules in neurons, together with manipulations of the relevant molecular motor proteins such as cytoplasmic dynein and kinesin-5. These studies also include a strong focus on the microtubule-severing proteins, namely katanin and spastin. The studies are aimed at understanding how axons grow, how dendrites are differentiated, how axonal branches are formed, and how growth cones navigate to find their targets. We are using electron tomography to study the 3D organization of microtubules in cultured, migratory neurons. We predict that some microtubules have their minus ends in the centrosome but many will not, and we suspect that microtubules vary in length and slide against one another using molecular motor proteins. In particular, the role of Kinesin-5 in neuronal growth and migration will be studied. Aditi Falnikar, a graduate student in the Baas lab has spent 2 weeks in Boulder to prepare specimens, collect data and learn the programs for reconstruction and modeling